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Subject: Re: [RFC PATCH v6] virtio-video: Add virtio video device specification
Alexander Gordeev <alexander.gordeev@opensynergy.com> writes: > Hi Alexandre, > > On 27.12.22 08:31, Alexandre Courbot wrote: >> Hi Alexander, >> >> >> On Tue, Dec 20, 2022 at 1:59 AM Alexander Gordeev >> <alexander.gordeev@opensynergy.com> wrote: >>> Hello Alexandre, >>> >>> Thanks for the update. Please check my comments below. >>> I'm new to the virtio video spec development, so I may lack some >>> historic perspective. I would gladly appreciate pointing me to some >>> older emails explaining decisions, that I might not understand. I hope >>> to read through all of them later. Overall I have a lot of experience in >>> the video domain and in virtio video device development in Opsy, so I >>> hope, that my comments are relevant and useful. >> Cornelia provided links to the previous versions (thanks!). Through >> these revisions we tried different approaches, and the more we >> progress the closer we are getting to the V4L2 stateful >> decoder/encoder interface. <snip> >> This probably means a bit more work on the device side, since this >> spec is tailored for the specific video codec use-case and V4L2 is >> more generic, but also less spec to maintain and more confidence that >> things will work as we want in the real world. On the other hand, the >> device would also become simpler by the fact that responses to >> commands could not come out-of-order as they currently do. So at the >> end of the day I'm not even sure this would result in a more complex >> device. > > Sorry for the delay. I tried to gather data about how the spec has > evolved in the old emails. > > Well, on the one hand mimicking v4l2 looks like an easy solution from > virtio-video spec writing perspective. (But the implementers will have > to read the V4L2 API instead AFAIU, which is probably longer...) > > On the other hand v4l2 has a lot of history. It started as a camera API > and gained the codec support later, right? So it definitely has just to > much stuff irrelevant for codecs. Here we have an option to design from > scratch taking the best ideas from v4l2. We definitely don't want to bake in Linux APIs into the VirtIO spec which is meant to be host/guest agnostic if we can help it. > > Also I have concerns about the virtio-video spec development. This seems > like a big change. It seems to me that after so many discussions and > versions of the spec, the process should be coming to something by now. > But this is still a moving target... > > There were arguments against adding camera support for security and > complexity reasons during discussions about virtio-video spec v1. Were > these concerns addressed somehow? Maybe I missed a followup > discussion? I think adding camera support would introduce a lot of potential complexity to the spec - c.f. projects like libcamera and the fact most modern cameras are more than providing a stream of images. It probably warrants having its own device specification that is designed from the outset with cameras in mind. -- Alex BennÃe Virtualisation Tech Lead @ Linaro
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